1. Field of the Invention
The invention relates to an adhesive substance for improved adhesion between a vulcanizable polymer and a metallic reinforcing carrier.
2. Background and Material Information
In order to produce a sufficient and long-lasting adhesion of rubber to metal, many parameters have to be taken into consideration. The surface of the metallic reinforcing carrier has to be modified so that the rubber is permitted to adhere. To that end, up till this point, metallic reinforcing carriers (generally steel cord), which were to be imbedded in rubber mixtures that could be vulcanized with sulfur, were coated with a layer of brass. Further developments were made in which the brass was replaced by zinc-cobalt or zinc-nickel alloys (EP 536 545). The brass layer or zinc alloy is used to produce a mechanical denticulation with the rubber layer during the vulcanization through the formation of an intermediary layer. However, there is a disadvantage in that the intermediary layer does not cover the metallic reinforcing carrier (steel cord) in all places so that these places represent weak points in the adhesion. Furthermore, additional sulfur is required for the production of the intermediary layer and must also be added to the rubber mixture. In order to produce a permanent adhesion between rubber and metal, it is furthermore necessary for the rubber mixture to be very resistant to aging. That is why mixtures containing cobalt salts were proposed. These rubber mixtures, though, had the disadvantage of low durability.
For rubber coatings of steel cord, it is furthermore known that the addition of resorcinol-formaldehyde condensation products should increase the aging resistance of the rubber mixture. These condensation products, however, are toxicologic which makes processing them more difficult.
A variety of experiments have already been conducted in order to optimize the adhesion between rubber and metal. As a rule, though, it is still necessary to match the reinforcing carrier and the rubber mixture of the adhesive mixture to each other within strict limits. This in turn has the disadvantage that with the combination of another adjoining rubber layer, the composition of this must be adapted to that of the adhesive mixture and consequently can only be varied within strict limits. A variation of the rubber composition, though, has an effect on the properties of the rubber product so that they, too, cannot be optimally adjusted. The requirement for producing a long-lasting and stable adhesion to the steel cord thus limits the freedom to optimize other desirable mixture properties.